1. Field of the Invention
This invention relates to a method and apparatus for filling a mold, and in particular to a method and apparatus for filling the heel cavity of a mold used in a slush molding machine for manufacturing articles of footwear.
2. Description of the Prior Art
The A. Cervinka Canadian Pat. Nos. 592,262 and 594,464, issued Feb. 9, 1960 and Mar. 15, 1960, respectively, describe the production of calf-length boots using a slush molding process in which a mold in the shape of the boot is filled with a plastisol, e.g. polyvinyl chloride, the mold is heated to cause the plastisol to gel and form a skin, excess plastisol is poured from the mold, and the mold is again heated to cure the plastisol.
As mentioned in applicant's Canadian Pat. No. 995,866, issued Aug. 31, 1976, when molding winter boots or the like with large heels, difficulties may be experienced in filling the heel cavity. It is necessary to fill the heel cavity exactly; otherwise, the finished product is uncomfortable to the point of being useless. Canadian Pat. No. 995,866 describes an automatic heel filling device which includes a dispenser mounted on the molding machine and capable of travelling with the mold for filling the heel cavity. The device utilizes a heat-hardenable plastisol, which fills the heel cavity and is cured with the skin.
It has been found that use of the slush molding method and machine described above with a heat-hardenable plastisol results in a large quantity of waste. Following formation of the skin, the top of the skin is removed by cutting to form a straight top edge of the boot. The excess skin is discarded as waste, and the skin is further processed, i.e. provided with a liner and otherwise finished to provide a boot. With a continuous slush molding process, large quantities of thermoplastic material are discarded as waste. Moreover, it is necessary to provide a separate plastisol for filling the heel.
Accordingly, a method and apparatus which utilize such waste thermoplastic material have obvious advantages. It has been found that in order to re-use the waste thermoplastic material, it must be made liquid and remain in liquid form until it is dispensed into the heel cavity of the mold. Liquification is achieved by grinding the waste thermoplastic material, possibly mixing it with a stabilizer and heating the resulting mixture to form a flowable thermoplastic mass. Once the mixture has been heated, it must remain heated until it is dispensed into the mold. Thus, the heel filling device described in Canadian Pat. No. 995,866 cannot be used to fill heel cavities with the thermoplastic mass, since the mixture would cool during passage to the mold.
The object of the present invention is to provide a method and apparatus which permit the use of waste plastisol for filling the heel cavity in a slush molding process.